Wireless telecommunication systems are well known in the art. In order to provide global connectivity for wireless systems, standards have been developed and are being implemented. One current standard in widespread use is known as Global System for Mobile Telecommunications (GSM). This is considered as a so-called Second Generation mobile radio system standard (2G) and was followed by its revision (2.5G). GPRS and EDGE are examples of 2.5G technologies that offer relatively high speed data service on top of (2G) GSM networks. Each one of these standards sought to improve upon the prior standard with additional features and enhancements. In January 1998, the European Telecommunications Standard Institute—Special Mobile Group (ETSI SMG) agreed on a radio access scheme for Third Generation Radio Systems called Universal Mobile Telecommunications Systems (UMTS). To further implement the UMTS standard, the Third Generation Partnership Project (3GPP) was formed in December 1998. 3GPP continues to work on a common third generational mobile radio standard.
A typical UMTS system architecture in accordance with current 3GPP specifications is depicted in FIG. 1. The UMTS network architecture includes a Core Network (CN) interconnected with a UMTS Terrestrial Radio Access Network (UTRAN) via an interface known as Iu which is defined in detail in the current publicly available 3GPP specification documents. The UTRAN is configured to provide wireless telecommunication services to users through wireless transmit receive units (WTRUs), known as User Equipments (UEs) in 3GPP, via a radio interface known as Uu. The UTRAN has one or more Radio Network Controllers (RNCs) and base stations, known as Node Bs in 3GPP, which collectively provide for the geographic coverage for wireless communications with UEs. One or more Node Bs is connected to each RNC via an interface known as Iub in 3GPP. The UTRAN may have several groups of Node Bs connected to different RNCs; two are shown in the example depicted in FIG. 1. Where more than one RNC is provided in a UTRAN, inter-RNC communication is performed via an Iur interface.
Communications external to the network components are performed by the Node Bs on a user level via the Uu interface and the CN on a network level via various CN connections to external systems.
In general, the primary function of base stations, such as Node Bs, is to provide a radio connection between the base stations' network and the WTRUs. Typically a base station emits common channel signals allowing non-connected WTRUs to become synchronized with the base station's timing. In 3GPP, a Node B performs the physical radio connection with the UEs. The Node B receives signals over the Jub interface from the RNC that controls the radio signals transmitted by the Node B over the Uu interface.
A CN is responsible for routing information to its correct destination. For example, the CN may route voice traffic from a UE that is received by the UMTS via one of the Node Bs to a public switched telephone network (PSTN) or packet data destined for the Internet. In 3GPP, the CN has six major components: 1) a serving General Packet Radio Service (GPRS) support node; 2) a gateway GPRS support node; 3) a border gateway; 4) a visitor location register; 5) a mobile services switching center; and 6) a gateway mobile services switching center. The serving GPRS support node provides access to packet switched domains, such as the Internet. The gateway GPRS support node is a gateway node for connections to other networks. All data traffic going to other operator's networks or the internet goes through the gateway GPRS support node. The border gateway acts as a firewall to prevent attacks by intruders outside the network on subscribers within the network realm. The visitor location register is a current serving networks ‘copy’ of subscriber data needed to provide services. This information initially comes from a database which administers mobile subscribers. The mobile services switching center is in charge of ‘circuit switched’ connections from UMTS terminals to the network. The gateway mobile services switching center implements routing functions required based on current location of subscribers and also receives and administers connection requests from subscribers from external networks.
The RNCs generally control internal functions of the UTRAN. The RNCs also provide intermediary services for communications having a local component via a Uu interface connection with a Node B and an external service component via a connection between the CN and an external system, for example overseas calls made from a cell phone in a domestic UMTS. Typically an RNC oversees multiple base stations, manages radio resources within the geographic area of wireless radio service coverage serviced by the Node Bs and controls the physical radio resources for the Uu interface. In 3GPP, the Iu interface of an RNC provides two connections to the CN: one to a packet switched domain and the other to a circuit switched domain. Other important functions of the RNCs include confidentiality and integrity protection.
The Uu radio interface of a 3GPP communications system uses Transport Channels (TrCH) for transfer of user data and signaling between UEs and Node Bs. In 3GPP communications, TrCH data is conveyed by one or more physical channels defined by mutually exclusive physical resources. TrCH data is transferred in sequential groups of Transport Blocks (TB) defined as Transport Block Sets (TBS). Each TBS is transmitted in a given Transmission Time Interval (TTI) which may span a plurality of consecutive system time frames. A typical system time frame is 10 milliseconds and TTIs are currently specified as spanning 1, 2, 4 or 8 of such time frames. U.S. patent application Ser. No. 10/417,586 entitled RECEIVING STATION FOR CDMA WIRELESS SYSTEM AND METHOD published as Publication No. US-2003-0198210-A1 on Oct. 23, 2003, owned by the assignee of the present invention describes the details of a receiver for such signals.
FIG. 2 illustrates the processing in preparation for transmission of uplink TrCHs in Frequency Division Duplex (FDD) mode into a Coded Composite TrCH (CCTrCH) and then into one or more physical channel data streams in accordance with 3GPP TS 25.212 v4.1.0. Starting with the TB of data, Cyclic Redundancy Check (CRC) bits are attached. TB concatenation and code block segmentation is then performed. Channel coding in the form of convolution coding or turbo coding is then performed, but in some instances no coding is specified. The steps after coding include radio frame equalization, a first interleaving, radio frame segmentation and rate matching. The radio frame segmentation divides the data over the number of frames in the specified TTI. The rate matching function operates by means of bit repetition or puncturing and defines the number of bits for each processed TrCH which are thereafter multiplexed to form a CCTrCH data stream.
The processing of the CCTrCH data stream includes physical channel segmentation when more than one physical channel is to be used, a second interleaving and mapping onto the one or more physical channels being used for the TTI per the TFC. The number of physical channels corresponds to the physical channel segmentation. Each physical channel data stream is then spread with a format-defined channelization code and spreading factor and modulated for over air transmission on an assigned frequency.
In FDD uplink, the number of physical channels and the respective spreading parameters per CCTrCH are dynamic link parameters which are chosen by the rate matching algorithm on a TTI-by-TTI basis based on the instantaneous amount of data that is to be transmitted. The range of values which these two parameters can take on is limited by the allowed transport format combinations (TFCs) which are negotiated during link setup. The set of allowed combinations is referred to as the Transport Format Combination Set (TFCS). The TFC selected for a given CCTrCH defines the number of PhCHs to be used and the respective spreading code and spreading factor for each PhCH. This information can be transmitted via a transport format combination indicator (TFCI) in the same frame as the data formatted according to the TFC. However, 3GPP specifications allow for the transmission of a TFCI to be omitted. Where a TFCI is transmitted, the TFCI data bits are selectively added to the CCTrCH data being mapped to each physical channel after the second interleaving. Examples of TrCH formatting for a 3GPP system are provided in TR 25.944 V4.1.0.
In the reception/decoding of the TrCH data, the processing is essentially reversed by the receiving station. Accordingly, UE and Node B physical reception of TrCHs require knowledge of TrCH processing parameters to reconstruct the TBS data. Receiving station processing is facilitated by the transmission of the TFCI for a CCTrCH. 3GPP provides for “blind transport format detection” (BTFD) by the receiving station, such as where the TFCI is not transmitted, in which case the receiving station considers the potential valid TFCIs for the particular type of channel being received. Where there is only one valid TFCI, that TFCI is used in either case.
In the case of UMTS W-CDMA uplink transmissions, signals are received from multiple UEs by a Node B base station in a plurality of physical channels. The data in each physical channel is received in spread form and must be de-spread. The physical channel (PhCH) portion of the receiver performs the de-spreading where each PhCH is despread using a received chip rate processor (RCRP) based upon the spreading code used by the transmitter for the particular channel. After despreading data channel processing typically begins with the second de-interleaving stage where the data from each physical channel is de-interleaved independently.
Despreading and independent second de-interleaving each PhCH are accomplished without delay for systems where the number of PhCH is know as well as the respective spreading factor and spreading code for each PhCH. However, in wireless communications such as 3GPP FDD uplink, the number of physical channels per CCTrCH and respective spreading factors and spreading codes are dynamic parameters, and their exact values for a frame are carried within that same frame either implicitly or explicitly through the inclusion of a TFCI.
In data processing for the physical channel carrying a CCTrCH, the unavailability of information regarding the transport format is problematic. In order to use existing methods of data processing communication data in 3GPP systems, unspread data in the form of chip samples for each frame can be buffered in a memory creating a one time frame period delay. The spreading factors, codes and the number of physical channels are then determined by either evaluating a transmitted TFCI within the buffered frame or through BTFD adding a small time fraction. The buffered chip samples for the frame are then despread using an RCRP based upon the determined spreading factors, spreading codes and the number of physical channels to produce data for each physical channel for second de-interleaving.
In order to conduct the de-interleaving processing, the de-interleaver requires the entire despread frame of data. Thus a second one time frame period delay is required before de-interleaving can commence. Not only does this processing include the substantial processing delay of two time frame periods, but the buffering of entire frames of chip samples requires substantial amounts of memory, particularly where sampling is done at twice the chip rate and the received signal is processed in both in-phase and quadrature components as is typical with 3GPP systems.
It is desirable to provide a receiver capable of efficient data processing of a composite channel when knowledge of the transport format is not available. In particular, it would be highly beneficial to avoid the buffering of entire frames of chip samples and the inherent two time frame delay in processing such signals.